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Wire Bonding

Tape Automated Bonding (TAB), Direct Chip Attachment (DCA), and wire bonding are the options available to interconnect MEMS die. While there are many subsets and derivatives, all IC interconnections can be classified into one of these three basic systems [28]. This section covers the most commonly used method of chip connection, wire bonding. Most often, this technique uses small gold wires; how­ever, aluminum or occasionally copper are also used. Wire diameters range from 15 (im to several hundred micrometers. There are two main classes of wire bond­ing: ball and wedge. Ball bonding is used with gold or copper wires and requires modestly elevated temperatures. Gold wires are far more common since its does not oxidize to impede micro-welding. Both gold and aluminum wires are used for wedge bonding, with heat being required only for gold. In wire bonding, the wire is attached at both ends using some combination of heat, pressure, and ultrasonic energy to make a weld. It is generally considered the most cost-effective and ver­satile interconnect technology. Wire materials properties that affect wire bonding include yield strength, ultimate tensile strength, elongation, and purity.

12.5.1 Gold Wire Bonding

Gold wires are used extensively for thermocompression and thermosonic bonding. As such, most common systems involve placing gold wires between a package and the aluminum bond pads on an IC; with RF devices, gold ribbons are often used to control parasitic inductance. It is the purity of the gold that controls the mechanical

Diameter Elongation (%) Break strength (g) minimum Elongation Break strength (g) minimum Elongation (%) Break strength (g) minimum
Automatic g old wire bonding          
0.0007" 0.5-2 2-5 45.8 5.8 3.5
0.0008" 0.5-2 2-5 5.5 5-8
0.0009" 0.5-2 2-5 6.5 5-9
0.0010" 0.5-2 2-5 5-10
0.00125" 0.5-2 2-5 5-11
0.0015" 0.5-3 2-5 5-12
0.002" 0.5-3 2-5 5-13
Manual gold wire bonding          
0.0007" 0.5-2 2-5 3.5 5.8 2.5
0.0008" 0.5-2 2-5 5-8
0.0009" 0.5-2 2-5 5.5 5-8
0.0010" 0.5-2 2-5 7.5 5-8 6.5
0.00125" 0.5-2 2-5 12.5 5-8
0.0015" 0.5-3 3-7 17.5 7-11 14.5
0.002" 0.5-3 3-7 7-11
Gold ribbon (bonded to 99% aluminum 1% silicon pad by thermosonic techniques)  
0.0007" 0.5-2 2-5 3.5 5.8 2.5
0.0008" 0.5-2 2-5 5-8
0.0009" 0.5-2 2-5 5.5 5-8
0.0010" 0.5-2 2-5 7.5 5-8 6.5
0.00125" 0.5-2 2-5 12.5 5-8
0.0015" 0.5-3 3-7 17.5 7-11 14.5
0.002" 0.5-3 3-7 7-11

 



properties of the wire, such as elongation and break strength. For example, small amounts, 5-10 ppm by weight, of beryllium or 20-100 ppm by weight of copper are added. Table 12.10 show typical wire strength values for automated system (HBX), manual system (HBXL), and ribbon wire bonds, respectively [29].


Date: 2015-02-28; view: 113


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